Ames
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ames clear sky chart from 2005-11-06 to 2025-08-05.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	12% 8% 3 8% 5% 4 4 4 6% 7% 39%	126020
	Night	11% 8% 3 8% 4 4 4 3 5% 7% 42%	122323
Transparency	Day	42% 6% 13% 24% 14% 1	129621
	Night	41% 5% 13% 24% 15% 2	126798
Seeing	Day	15% 10% 30% 28% 14% 3	16916
	Night	15% 9% 33% 31% 11% 1	26744

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	6% 12% 6% 21% 8% 6% 5% 3 4 5% 24%	3617
	11th to 20th	Day	6% 10% 4 11% 6% 7% 8% 5% 7% 7% 29%	4052
	21st to end	Day	10% 13% 7% 13% 6% 5% 4 3 5% 5% 30%	4488
February	1st to 10th	Day	10% 14% 5% 11% 7% 5% 5% 4 6% 8% 28%	1800
	11th to 20th	Day	11% 10% 4 8% 6% 6% 5% 3 5% 6% 35%	1754
	21st to end	Day	12% 10% 3 11% 5% 4 5% 3 5% 6% 36%	1586
March	1st to 10th	Day	16% 9% 3 6% 4 3 3 2 3 5% 46%	4936
	11th to 20th	Day	11% 7% 2 6% 4 3 4 3 5% 8% 47%	4980
	21st to end	Day	20% 13% 5% 8% 5% 4 4 4 5% 6% 26%	5462
April	1st to 10th	Day	18% 10% 3 6% 5% 5% 4 4 5% 7% 34%	2389
	11th to 20th	Day	17% 9% 3 7% 6% 5% 3 3 5% 7% 35%	2374
	21st to end	Day	21% 8% 3 6% 4 4 5% 3 5% 6% 34%	2552
May	1st to 10th	Day	14% 7% 3 7% 4 4 5% 3 6% 7% 39%	5862
	11th to 20th	Day	15% 6% 2 6% 4 3 3 3 5% 7% 46%	6243
	21st to end	Day	14% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	6935
June	1st to 10th	Day	10% 6% 2 6% 4 5% 5% 4 6% 8% 45%	2800
	11th to 20th	Day	9% 6% 2 5% 5% 4 4 4 7% 10% 44%	2800
	21st to end	Day	9% 7% 2 6% 6% 5% 5% 5% 7% 8% 40%	2800
July	1st to 10th	Day	8% 6% 2 6% 4 5% 5% 5% 8% 10% 41%	6360
	11th to 20th	Day	8% 5% 2 6% 4 4 4 4 6% 7% 50%	6323
	21st to end	Day	8% 5% 2 7% 5% 5% 6% 5% 7% 9% 42%	6422
August	1st to 10th	Day	8% 5% 2 6% 4 4 5% 5% 6% 9% 46%	4157
	11th to 20th	Day	13% 7% 2 6% 5% 5% 5% 4 7% 8% 39%	4041
	21st to end	Day	7% 5% 2 7% 5% 5% 4 4 6% 8% 48%	4276
September	1st to 10th	Day	11% 5% 2 4 4 4 3 4 4 7% 53%	2280
	11th to 20th	Day	10% 5% 1 6% 4 4 4 4 7% 7% 49%	2216
	21st to end	Day	12% 4 2 6% 4 3 5% 3 5% 7% 49%	2019
October	1st to 10th	Day	14% 6% 3 6% 4 4 4 2 5% 6% 48%	1900
	11th to 20th	Day	15% 7% 3 6% 4 4 3 4 4 5% 45%	1900
	21st to end	Day	15% 8% 3 7% 4 3 3 3 5% 7% 42%	2090
November	1st to 10th	Day	10% 7% 2 6% 5% 4 4 4 6% 7% 44%	1806
	11th to 20th	Day	14% 10% 4 6% 5% 3 4 5% 5% 8% 38%	1600
	21st to end	Day	14% 10% 4 6% 4 5% 5% 3 4 7% 38%	1600
December	1st to 10th	Day	7% 7% 3 7% 4 4 4 4 5% 8% 47%	2610
	11th to 20th	Day	14% 10% 4 14% 6% 6% 5% 4 5% 6% 26%	3008
	21st to end	Day	21% 18% 8% 13% 5% 3 4 2 4 4 18%	3982
January	1st to 10th	Night	9% 11% 5% 20% 7% 4 4 3 5% 6% 26%	6348
	11th to 20th	Night	9% 11% 4 9% 7% 5% 7% 4 7% 7% 30%	5924
	21st to end	Night	10% 13% 5% 12% 5% 4 4 3 5% 6% 31%	6490
February	1st to 10th	Night	10% 13% 4 11% 7% 4 4 4 4 7% 32%	2600
	11th to 20th	Night	11% 9% 4 8% 4 5% 5% 3 5% 6% 40%	2533
	21st to end	Night	11% 8% 4 9% 5% 4 3 3 5% 6% 43%	2058
March	1st to 10th	Night	15% 8% 2 5% 2 2 3 3 4 6% 50%	4922
	11th to 20th	Night	9% 6% 2 5% 4 3 4 3 5% 8% 51%	4980
	21st to end	Night	18% 11% 5% 11% 5% 5% 4 3 5% 5% 28%	5467
April	1st to 10th	Night	14% 8% 3 6% 5% 4 3 4 4 7% 42%	2010
	11th to 20th	Night	14% 9% 2 7% 4 4 4 3 5% 6% 41%	1975
	21st to end	Night	16% 8% 2 7% 4 4 4 3 5% 6% 42%	1845
May	1st to 10th	Night	15% 6% 2 5% 3 3 3 3 5% 6% 48%	4053
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 4 7% 52%	3670
	21st to end	Night	16% 7% 3 6% 5% 4 4 3 5% 6% 41%	3942
June	1st to 10th	Night	6% 5% 2 6% 4 5% 4 4 6% 7% 51%	1600
	11th to 20th	Night	7% 6% 2 6% 5% 4 4 3 6% 10% 47%	1600
	21st to end	Night	8% 5% 2 5% 4 5% 5% 4 5% 7% 50%	1600
July	1st to 10th	Night	7% 4 2 5% 4 4 5% 4 8% 10% 48%	3618
	11th to 20th	Night	6% 4 2 4 3 4 4 4 6% 9% 55%	3651
	21st to end	Night	7% 4 2 5% 4 5% 5% 5% 8% 9% 46%	4449
August	1st to 10th	Night	5% 4 2 5% 4 4 4 4 5% 10% 53%	2872
	11th to 20th	Night	9% 5% 2 5% 4 3 3 3 4 8% 56%	2798
	21st to end	Night	8% 5% 2 5% 3 3 3 3 4 7% 55%	3383
September	1st to 10th	Night	9% 5% 2 5% 3 3 3 2 4 5% 58%	1900
	11th to 20th	Night	10% 5% 2 4 3 3 4 2 5% 6% 56%	1962
	21st to end	Night	9% 5% 1 4 3 3 3 3 5% 6% 59%	2142
October	1st to 10th	Night	11% 7% 2 5% 3 3 3 3 4 6% 53%	2280
	11th to 20th	Night	15% 6% 2 6% 3 3 3 3 4 6% 49%	2280
	21st to end	Night	15% 9% 2 5% 3 3 4 3 4 6% 44%	2508
November	1st to 10th	Night	11% 6% 2 5% 3 3 3 3 5% 6% 52%	2488
	11th to 20th	Night	12% 9% 2 7% 4 4 4 5% 5% 6% 42%	2800
	21st to end	Night	14% 9% 3 7% 4 3 4 4 5% 5% 42%	2800
December	1st to 10th	Night	6% 9% 3 7% 4 5% 4 4 6% 7% 45%	4580
	11th to 20th	Night	11% 10% 4 11% 6% 4 4 4 5% 6% 34%	5199
	21st to end	Night	20% 16% 7% 13% 5% 4 3 3 4 4 20%	6996

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	61% 6% 12% 15% 6%	3618
	11th to 20th	Day	52% 4 11% 18% 14% 1	4052
	21st to end	Day	56% 4 13% 20% 7%	4488
February	1st to 10th	Day	55% 5% 14% 18% 8% 1	1800
	11th to 20th	Day	49% 6% 10% 21% 11% 2	1763
	21st to end	Day	49% 5% 14% 18% 12% 3	1586
March	1st to 10th	Day	42% 4 10% 26% 17% 2	4936
	11th to 20th	Day	35% 5% 9% 30% 18% 2	4980
	21st to end	Day	58% 6% 15% 15% 4 1	5464
April	1st to 10th	Day	49% 6% 11% 24% 10% 1	2389
	11th to 20th	Day	48% 6% 12% 21% 13% 1	2374
	21st to end	Day	48% 6% 11% 22% 11% 1	2552
May	1st to 10th	Day	42% 6% 12% 22% 17% 1	5900
	11th to 20th	Day	37% 6% 11% 27% 17% 3	6247
	21st to end	Day	43% 7% 13% 23% 14% 1	6949
June	1st to 10th	Day	36% 8% 16% 24% 15% 2	2800
	11th to 20th	Day	33% 7% 15% 24% 19% 2	2800
	21st to end	Day	38% 8% 15% 23% 14% 2	2800
July	1st to 10th	Day	36% 7% 15% 32% 9% 1	6291
	11th to 20th	Day	32% 6% 14% 31% 16% 1	6248
	21st to end	Day	35% 8% 18% 26% 13% 1	6240
August	1st to 10th	Day	33% 7% 16% 29% 15% 1	4143
	11th to 20th	Day	42% 6% 14% 25% 13% 1	4080
	21st to end	Day	33% 6% 16% 26% 17% 2	4275
September	1st to 10th	Day	31% 6% 12% 27% 20% 4	2280
	11th to 20th	Day	32% 6% 14% 30% 17% 1	2216
	21st to end	Day	34% 6% 11% 31% 19% 1	2019
October	1st to 10th	Day	23% 3 6% 29% 37% 2	3160
	11th to 20th	Day	29% 3 9% 30% 25% 4	3140
	21st to end	Day	39% 4 10% 29% 15% 3	3428
November	1st to 10th	Day	37% 6% 16% 22% 17% 2	1806
	11th to 20th	Day	43% 5% 15% 21% 15% 1	1600
	21st to end	Day	46% 4 15% 24% 10% 1	1600
December	1st to 10th	Day	35% 4 16% 36% 8% 1	2610
	11th to 20th	Day	57% 5% 14% 16% 7%	3005
	21st to end	Day	70% 4 8% 13% 4	3982
January	1st to 10th	Night	59% 4 14% 14% 8% 1	6348
	11th to 20th	Night	50% 4 14% 14% 16% 2	5924
	21st to end	Night	52% 5% 12% 18% 13% 1	6490
February	1st to 10th	Night	52% 5% 12% 21% 10% 1	2600
	11th to 20th	Night	44% 6% 11% 24% 13% 2	2534
	21st to end	Night	43% 4 12% 21% 17% 3	2058
March	1st to 10th	Night	36% 4 9% 31% 19% 2	4922
	11th to 20th	Night	32% 4 9% 33% 18% 4	4980
	21st to end	Night	56% 7% 15% 15% 5% 2	5467
April	1st to 10th	Night	41% 6% 12% 25% 14% 2	2010
	11th to 20th	Night	43% 5% 11% 21% 17% 2	1975
	21st to end	Night	43% 5% 13% 23% 14% 2	1845
May	1st to 10th	Night	36% 6% 11% 27% 20% 1	4080
	11th to 20th	Night	33% 5% 11% 27% 18% 5%	3671
	21st to end	Night	42% 6% 12% 23% 15% 2	3950
June	1st to 10th	Night	30% 7% 16% 28% 16% 4	1600
	11th to 20th	Night	31% 7% 14% 22% 22% 5%	1600
	21st to end	Night	30% 7% 14% 27% 18% 4	1600
July	1st to 10th	Night	29% 6% 16% 32% 15% 1	3580
	11th to 20th	Night	26% 6% 16% 32% 18% 2	3606
	21st to end	Night	31% 9% 19% 25% 14% 1	4320
August	1st to 10th	Night	27% 6% 17% 33% 15% 2	2862
	11th to 20th	Night	30% 5% 17% 31% 16% 1	2825
	21st to end	Night	28% 6% 16% 28% 17% 5%	3383
September	1st to 10th	Night	28% 4 11% 27% 25% 4	1900
	11th to 20th	Night	29% 4 12% 34% 20% 1	1962
	21st to end	Night	27% 5% 10% 31% 24% 3	2142
October	1st to 10th	Night	22% 3 6% 25% 41% 3	3800
	11th to 20th	Night	27% 3 8% 28% 26% 7%	3779
	21st to end	Night	41% 4 10% 25% 17% 2	4120
November	1st to 10th	Night	33% 4 16% 26% 18% 4	2488
	11th to 20th	Night	40% 5% 15% 25% 14% 2	2800
	21st to end	Night	44% 4 12% 26% 13% 1	2800
December	1st to 10th	Night	37% 4 13% 37% 8%	4580
	11th to 20th	Night	50% 5% 14% 25% 6%	5201
	21st to end	Night	68% 5% 10% 13% 5%	6996

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	17% 12% 37% 25% 7% 2	300
	11th to 20th	Day	17% 12% 45% 21% 4	300
	21st to end	Day	17% 12% 38% 27% 4 1	330
February	1st to 10th	Day	16% 21% 38% 20% 3 1	300
	11th to 20th	Day	16% 18% 36% 25% 5%	300
	21st to end	Day	19% 15% 44% 18% 4	249
March	1st to 10th	Day	18% 15% 42% 17% 6% 1	300
	11th to 20th	Day	23% 13% 35% 22% 7%	300
	21st to end	Day	33% 14% 32% 16% 4	330
April	1st to 10th	Day	25% 16% 34% 19% 5%	489
	11th to 20th	Day	24% 15% 33% 19% 8% 1	492
	21st to end	Day	25% 15% 31% 21% 7% 2	652
May	1st to 10th	Day	21% 12% 32% 22% 11% 2	703
	11th to 20th	Day	22% 13% 27% 23% 13% 2	725
	21st to end	Day	17% 8% 27% 30% 14% 3	789
June	1st to 10th	Day	8% 8% 26% 32% 22% 4	730
	11th to 20th	Day	11% 6% 28% 37% 15% 3	730
	21st to end	Day	11% 8% 32% 32% 15% 3	730
July	1st to 10th	Day	9% 4 17% 35% 25% 10%	721
	11th to 20th	Day	7% 3 27% 34% 23% 7%	718
	21st to end	Day	6% 2 23% 38% 25% 5%	794
August	1st to 10th	Day	8% 5% 19% 36% 26% 5%	697
	11th to 20th	Day	14% 3 17% 36% 23% 6%	665
	21st to end	Day	11% 3 21% 35% 23% 7%	596
September	1st to 10th	Day	13% 5% 23% 32% 21% 6%	490
	11th to 20th	Day	9% 4 23% 38% 21% 6%	426
	21st to end	Day	12% 10% 27% 32% 15% 4	300
October	1st to 10th	Day	16% 6% 31% 25% 17% 4	300
	11th to 20th	Day	17% 19% 34% 22% 7% 1	300
	21st to end	Day	20% 14% 37% 21% 6% 3	330
November	1st to 10th	Day	18% 11% 38% 23% 8% 2	300
	11th to 20th	Day	18% 21% 32% 19% 8% 1	300
	21st to end	Day	21% 13% 38% 23% 4 1	300
December	1st to 10th	Day	11% 14% 46% 20% 8% 1	300
	11th to 20th	Day	15% 16% 35% 24% 9% 1	300
	21st to end	Day	24% 16% 39% 17% 2 1	330
January	1st to 10th	Night	14% 12% 37% 30% 7%	1000
	11th to 20th	Night	16% 13% 36% 28% 6% 1	1000
	21st to end	Night	17% 12% 36% 29% 6%	1100
February	1st to 10th	Night	17% 11% 39% 28% 5%	1000
	11th to 20th	Night	16% 13% 40% 26% 5%	979
	21st to end	Night	16% 13% 42% 24% 4 1	738
March	1st to 10th	Night	19% 11% 38% 24% 7% 1	603
	11th to 20th	Night	18% 9% 38% 27% 8%	600
	21st to end	Night	24% 12% 39% 18% 7% 1	660
April	1st to 10th	Night	19% 14% 40% 23% 4	600
	11th to 20th	Night	19% 12% 36% 27% 6% 1	593
	21st to end	Night	19% 11% 36% 26% 8% 1	600
May	1st to 10th	Night	18% 8% 34% 32% 9% 1	600
	11th to 20th	Night	16% 9% 32% 30% 11% 1	591
	21st to end	Night	16% 7% 27% 36% 13%	650
June	1st to 10th	Night	8% 4 29% 41% 18%	600
	11th to 20th	Night	11% 4 28% 45% 11% 1	600
	21st to end	Night	9% 5% 32% 38% 16%	600
July	1st to 10th	Night	7% 1 14% 47% 28% 2	585
	11th to 20th	Night	6% 1 22% 44% 25% 2	582
	21st to end	Night	6% 3 18% 49% 23% 1	657
August	1st to 10th	Night	7% 3 15% 47% 25% 2	579
	11th to 20th	Night	8% 2 16% 46% 24% 3	564
	21st to end	Night	10% 2 22% 41% 24% 2	627
September	1st to 10th	Night	13% 4 21% 38% 22% 2	570
	11th to 20th	Night	12% 3 24% 39% 20% 2	570
	21st to end	Night	12% 5% 31% 36% 14% 1	622
October	1st to 10th	Night	14% 8% 32% 31% 14% 1	760
	11th to 20th	Night	17% 12% 34% 30% 7%	760
	21st to end	Night	21% 9% 34% 28% 7%	836
November	1st to 10th	Night	14% 10% 37% 30% 8%	818
	11th to 20th	Night	17% 14% 40% 22% 6%	1000
	21st to end	Night	17% 13% 36% 27% 8%	1000
December	1st to 10th	Night	15% 13% 37% 29% 6%	1000
	11th to 20th	Night	19% 9% 35% 31% 6%	1000
	21st to end	Night	24% 11% 37% 23% 5%	1100

Page generated at 2025-08-02 00:32:23. Version ac07

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